Where does freshwater and saltwater mix?

Where does freshwater and saltwater mix?

• A. Desert oasis
• B. Mountain watershed
• C. Estuary
• D. Glacier

Answer: (C)

Estuaries are places where freshwater from rivers meets seawater and mixes under tidal action. The river brings low-salinity water toward the coast, while the ocean supplies higher-salinity water from offshore. The tug-of-war between these flows creates a salinity gradient: the water near the river mouth can be brackish, transitioning from nearly fresh upstream to saline closer to the sea. Tides stir and mix these waters, and the resulting gradient supports unique ecosystems, nursery habitats, and nutrient cycling. Other options don’t involve the mixing of river freshwater with seawater. A desert oasis is groundwater that reaches the surface in an arid region, not the interface between river and ocean. A mountain watershed describes a land drainage area, not an estuary. A glacier is freshwater ice or meltwater, not a mixing zone with seawater.

Estuaries are places where freshwater from rivers meets seawater and mixes under tidal action. The river brings low-salinity water toward the coast, while the ocean supplies higher-salinity water from offshore. The tug-of-war between these flows creates a salinity gradient: the water near the river mouth can be brackish, transitioning from nearly fresh upstream to saline closer to the sea. Tides stir and mix these waters, and the resulting gradient supports unique ecosystems, nursery habitats, and nutrient cycling.

Other options don’t involve the mixing of river freshwater with seawater. A desert oasis is groundwater that reaches the surface in an arid region, not the interface between river and ocean. A mountain watershed describes a land drainage area, not an estuary. A glacier is freshwater ice or meltwater, not a mixing zone with seawater.